Ricerc@Sapienza

Recently Li-ion batteries (LIBs) had a great development because of their advantages with respect to traditional ones: they present higher energy and power density, moreover they last longer and have higher efficiency. For these reasons, their use has grown above all for portable electronics and hybrid/full electric vehicles.
However, the high energy content of these batteries poses safety problems. In recent years, several episodes have been reported in which LIBs have been the source of fires and dangerous accidents. This is due to their high energy density which imply greater danger in the event of malfunctions or failures, given the presence of toxic and highly flammable substances. In the worst case a thermal runaway can occur. Any abuse, for example exposure to fire, overcharging, short- circuiting or crushing, can be a trigger for spontaneous self-heating reactions which can result in a fire, and eventually an explosion. The variables that affect the fire behavior of the batteries are various, in particular chemical composition of components (e.g. anode, cathode, electrolyte) vary among LIBs.
The purpose of this project is to examine the response to thermal abuse tests of 18650 cells. In particular, the aim is to study the influence of electrical formation cycle (a sequence of charge and discharge cycles that guarantees an adequate stabilization of the cells performance) and its impact on the behavior of the cell when exposed to an external heat flux. Heat release rate, surface temperature, mass loss and VOC concentration are measured using a cone calorimeter and a photoionization detector.
Cell components before and after the tests are then characterized by using different techniques such as DSC, XRD and SEM. With regard to the residues after tests, the purpose is to identify the composition of components and their role in re-ignition of fire, in fact several documented cases are reported of battery pack subject again to fire after its extinction.